1. Field of the Invention
This invention relates to an ink, an ink-jet ink, a method for decreasing kogation on the surface of a heater for heat application to the ink, a method for ink-jet recording, an ink-jet recording apparatus, a recording unit, and a method for increasing life of the ink-jet recording head.
2. Related Background Art
There have been proposed various types of ink-jet recording method. According to an ink-jet recording method, such as the so-called bubble-jet recording method described in, for example, Japanese Patent Application Laid-Open No. 54-51837, ink is ejected in the form of ink droplets by the action of thermal energy. A feature of the ink-jet method is that high quality images can be formed on plain paper having no special coating layer at high speed and at low cost, due to the very simple structure of the high-density multinozzles. In this method, rapid heating of the heater in the recording head induce bubble generation in the liquid on the heater with rapid bubble volume inflation, and the action force due to this rapid volume increment ejects a liquid droplet from the nozzles arranged at the tip of the recording head to make the droplet fly to the recording material and attach thereon. Printing is thus carried out.
In this method, however, the heater in the recording head is repeatedly heated to eject ink during mass printing. This may cause the deposition of the decomposition product of the ink, the so-called kogation, on the surface of the heater. Deposition of koga prevents the efficient transmission of the thermal energy from the heater to the ink, resulting in the decrease in the volume and speed of the ejected droplets in comparison with the initial stage, which affects the image quality. In such a case, the recording head must be changed with a new one in order to continuously achieve high quality printing. To the users, this means a higher printing cost in total.
Thus, reduction of kogation on the heater in order to prolong the recording head life has been one of the important technical problems to be improved in the art of bubble-jet method. There has been proposed, for example, ink containing an oxoanion (Japanese Patent Application Laid-Open No. 3-160070), where as an oxoanion, described are phosphate salts, polyphosphates, phosphoric esters, arsenates, molybdates, sulfates, sulfites and oxalates.
However, when the ejection of such an ink is repeated, the above oxoanions in the ink may dissolve the outermost protection layer of the heater made of a metal such as tantlum and/or a metal oxide to cause wire breakage in the heater. In addition, such an ink is still insufficient in kogation prevention.
An object of the present invention is to provide an ink and a method for decreasing kogation on the surface of the heater which is used for applying thermal energy to the ink in a recording head so as to eject the above ink from the recording head.
Another object of the present invention is to provide an ink-jet recording method and ink-jet recording apparatus, which enables high quality printing and prolonged product life of the recording head.
A further object of the present invention is to provide a recording unit which enables high quality printing over a prolonged period.
Still another object of the present invention is to provide a method for prolonging the product life of the recording head to lower the cost in high quality printing.
According to one aspect of the present invention, there is provided an ink comprising:
(a) a coloring material,
(b) a liquid medium,
(c) a compound selected from the group consisting of polyphosphoric acid, dicarboxylic acid, polyaminocarboxylic acid, aldonic acid, hydroxycarboxylic acid, polyolphosphate and salts thereof, and
(d) an acid having an amino group and/or a salt thereof.
According to another aspect of the present invention, there is provided a method for reducing kogation on a surface of a heater of a recording head of an ink-jet printer, the heater being arranged to apply thermal energy to an ink in the recording head to eject the ink from an orifice in the recording head, and the heater having an outermost protection layer containing at least one of a metal and a metal oxide, the method comprising a step of using an ink as described above.
When an ink of the above composition and an ink jet printer of the above constitution are used for image formation, such an arrangement enables kogation reduction very effectively without dissolving the outermost surface of the heater which applies thermal energy for the ink ejection.
Although the reason why the use of this ink brings about good results is not clearly known, the inventors have confirmed that the combination use of the components (c) and (d) can reduce the kogation more than the single use of the component (c) or (d) does, elongating the head life. Thus, the components (c) and (d) seem to work synergetically in the ink. According to further study by the inventors, it is considered that the component (c) prevents kogation, or enhance koga decomposition or peeling off from the heater surface, and the component (d) functions in enhancing the head life by preventing the metal and/or metal oxide constituting the outermost protection surface of the heater from dissolving. Such an effect of the component (d) is especially remarkable with an ink containing an acid having a sulfonic group in addition to an amino group as the component (d), which satisfies both the kogation prevention effect and head life elongation effect at a very high level.
When the metal or the metal oxide contained in the outermost protection layer of the heater is tantalum or the oxide thereof, the effect is more remarkable. Further, effect of the present invention in preventing kogation will become more prominent, if the amount of the energy applied to the above heater is set so that Eop satisfies the relation in the following equation:
1.10xe2x89xa6Eop/Ethxe2x89xa61.90
wherein Eop denotes the amount of the energy applied to the above heater and Eth denotes the minimum energy required for ink ejection.
According to another aspect of the present invention, there is provided an ink-jet recording method which comprises a step of applying thermal energy to a heater to eject an ink from an orifice, wherein the ink is an ink as described above.
According to further aspect of the present invention, there is provided an ink-jet recording apparatus which comprises an ink container containing an ink, an ink jet-recording head having a heater to supply thermal energy to the ink in an ink flow path supplied from the ink container, and means for applying a pulse electric signal to the heater according to recorded information, wherein the heater has an outermost surface-protecting layer containing at least one of a metal and a metal oxide, and the ink is an ink as described above.
According to still another aspect of the present invention, there is provided a recording unit which comprises an ink container, and an ink jet-recording head having a heater to supply thermal energy to the ink in an ink flow path supplied from the ink container, wherein the heater has an outermost surface-protecting layer containing at least one of a metal and a metal oxide, and the ink is an ink as described above.
According to still another aspect of the present invention, there is provided a method for prolonging a life of a recording head equipped with a heater, the recording head being used in an ink-jet recording method comprising a step of ejecting ink through an opening by applying thermal energy to the ink,
wherein the heater is provided with an outermost protection layer containing at least a metal or oxide thereof and the ink is an ink as described above.